High-purity fluorine gas, the production and use thereof, and a method for monitoring impurities in a fluorine gas

ABSTRACT

An apparatus for producing a fluorine gas, comprising at least one fluorine generating cell, and at least one fluorine generating cell detector for detecting components of products obtained by the fluorine generating cell, wherein at least one of the fluorine generating cells is connected with the fluorine generating cell detector.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a U.S. national stage entry under 35 U.S.C. §371 of International Application No. PCT/EP2010/065334 filed Oct. 13, 2010, which claims priority to European Application No. 09173332.9 filed Oct. 16, 2009, the whole content of this application being incorporated herein by reference for all purposes.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a high-purity fluorine gas and the production thereof, an apparatus for producing a fluorine gas, and a method for monitoring and controlling impurities in a fluorine gas, and use thereof.

BACKGROUND OF THE INVENTION

Fluorine gas is an indispensable basic gas, and is used as an etching gas or a cleaning gas in the semiconductor industry, for the manufacture of photovoltaic cells and TFTs (thin film transistors) for liquid crystal displays because of its reaction properties. Particularly, in uses for annealing metal fluoride for optical materials or as a gas for an excimer laser, the optical properties of fluorine are also important and the amount of fluorine gas used for this purpose is increasing. Accompanying these demands, a high-purity fluorine gas is strongly required. For example, in the field of production of semiconductors, a fluorine gas having a high purity of 99.7% or more is demanded. In particularly, for optical uses, a high-purity fluorine gas reduced in impurities such as fluorocarbon, especially CF₄, and having a purity of 99.9 to 99.99 vol % is demanded. Therefore, for this purpose, the requirement for diminishing the amount of fluorocarbon, especially CF₄ a high-purity fluorine gas is increasing.

Generally, the fluorine gas supplied on a commercial basis contains about 1.5 vol % of impurities. The majority of the impurities are N₂, O₂, CO₂, fluorocarbons such as CF₄, and gases such as SF₆, SiF₄ and HF. In industrial manufacture, F₂ is produced by electrolysis of molten compositions comprising KF and HF, and carbon anodes are frequently used. In optimal operation conditions F₂ generating electrolysis cells produce less than 100 ppmv CF₄. But sometimes the fluorocarbon, especially CF₄ content in fluorine coming from a fluorine plant is much higher without a predictable or obvious reason. The daily practice showed that most times only one cell is responsible for increased CF₄ production with the effect that the whole fluorine production is contaminated. The fluorocarbon, especially CF₄ can be detected directly with FTIR (Fourier transform IR) spectroscopy, TDL (tunable diode laser) spectroscopy, GC (gas chromatography) and other methods with low detection limits in a wide concentration range. But the instruments are expensive, complex and need much space or cannot serve as a fast online analysis device (GC) or only with difficulties in installation with respect to small sample compartments or the need of an external detector (FTIR).

By a typical industrial fluorine generating electrolytic cell, a gas mixture is produced consisting of about 94 to 97 vol % fluorine, the rest is HF with only traces of the other impurities. If an anode “burn” occurs, the concentration of CF₄ is mostly elevated to values between 1 vol % and 10 vol %; COF₂ is elevated to concentrations up to some thousand ppmv; HF is slightly elevated. If OF₂ is present, its concentration is reduced.

The method described in U.S. Pat. No. 6,955,801 B2 is a method for producing of and analyzing impurities in a high-purity fluorine gas, comprising filling a fluoronickel compound in a container comprising a metal material or a metal material having a nickel film, said container having a fluorinated layer formed on a surface of the metal material or nickel film, conducting a step of heating the fluoronickel compound to 250 to 600° C., and reducing the pressure inside the container to 0.01 MPa (absolute pressure) or less, and a step of allowing a fluorine gas reduced in a hydrogen fluoride content to 500 vol ppm or less to be occluded into the fluoronickel compound passed through the first step, respectively, at least once, and further conducting said first step, then contacting a fluorine gas containing impurity gases with the fluoronickel compound at 200 to 350° C. to fix and remove the fluorine gas, and analyzing the impurities by GC or IR.

However, using this method, the post-processing treatment and the instructions needed are very complex, and expensive. Moreover, using this method, it is not possible to analyze fluorine gas and control the quality of fluorine gas obtained simply, especially, on-line, semi on-line or at-line.

It has now been found an apparatus for producing such high-purity fluorine gas, a method for the manufacture of high purity fluorine gas and an analysis method for the fluorine gas (especially, on-line analysis method).

SUMMARY OF THE INVENTION

The present invention now makes available an apparatus for producing a high-purity fluorine gas. Another object of the present invention is to provide a method for producing a high-purity fluorine gas, as well as a method for analyzing the compositions of fluorine gas obtained. Moreover, the present invention also relates to uses thereof. It has now been found in particular a fast, reliable, inexpensive and relatively small analyzer or analyzing method, which can be run on-line, semi on-line or at-line close to each F₂ generating electrolytic cell, to detect the fluorocarbon, especially CF₄ producing cell/cells immediately.

In general, the production of fluorine can be carried out in fluorine generating cell, wherein at the startup of a fluorine generating cell (in conditioning mode) the content of fluorine is measured by a detector system, especially, in the present invention, by FTIR and/or UV. The term “fluorine generating cell” (used for the sake of simplicity) denotes a fluorine generating electrolytic cell, i.e. a cell in which fluorine is produced electrolytically, usually by the electrolysis of a molten composition of KF and HF.

In these cells, often carbon anodes are applied for the transport of electric current. Such anodes sometimes unpredictably undergo anode burn. An anode burn in the fluorine generating cell is indicated by a slightly elevated HF content (for example, measured by FTIR) and an extremely elevated CF₄ content (the content of C₂F₆ and COF₂ also increase, while the OF₂ amount decreases, all monitored by a detector system, especially, in the present invention, by UV). During current efficiency measurements which, in the present invention, are performed preferably with a UV spectrometer, it has been surprisingly found that UV spectroscopy as a direct measurement tool only for fluorine shows a sharp decrease in fluorine concentration when an anode burn occurs. Therefore the burn can be detected easily by the sharp decrease of the F₂ concentration during the burn, during which impurities are formed (mainly CF₄ and COF₂). The result of this burn (more CF₄, C₂F₆, COF₂, HF, less OF₂) is not only the alteration of impurities' contents but also a sharp decrease in the content of fluorine monitored by a detector system, especially, in the present invention, by UV spectroscopy. During the measurement by UV spectroscopy, the whole UV spectrum can be used for measuring. Preferably, not the whole spectrum but only the absorption at this particular wavelength, particular UV spectroscopy with wavelengths between 200 and 400 nm, more preferred 250 to 330 nm, very preferred between 270 to 290 nm, especially preferably, between 275 and 285 nm, and even at about 280 nm is used for measuring, because it is more or less the maximum of the UV absorption of F₂. The spectrum may comprise all wavelengths in said range, or only selected wavelengths. It is also possible to use a UV light source which only emits a single wavelength in that range, several single wavelengths or a very narrow band, e.g. a UV light band with a breadth of 1 to 5 nm. Potential impurities, for example, CF₄, C₂F₆, COF₂, HF and OF₂ do not absorb at this range of wavelengths, so the decrease/increase of the F₂ concentration can selectively be monitored; the surprising feature is that anode burn is detected not by the increase of the CF₄ concentration, but by the decrease of the F₂ content of the produced gas.

When the burn is over, CF₄ (C₂F₆, COF₂, and HF) concentration starts to decrease again while the OF₂ amount starts to increase again. The end of the anode burn is also detectable by the rising of the fluorine content in the gas mixture leaving the cell.

Seen from the phases of the production of fluorine, if the anode burn is avoided, the impurities, for example, CF₄, C₂F₆, COF₂, HF and the like, can be decreased.

Particularly, in order to produce high-purity fluorine, immediately after detection of a decrease of the measured fluorine content (for example, more than 0.1 vol %, particular more than 0.3 vol %, or more than 0.5 vol %, even more than 1 vol %), the fluorine generating cell is separated from the production of the pure fluorine. This prevents a contamination of the produced fluorine with the impurities from the malfunctioning electrolytic cell. It is then observed if the fluorine content further decreases. If the fluorine content continues to decrease, the fluorine generating cell is shut down and cured (repaired); alternatively, the cell is kept producing fluorine which then is either destroyed, e.g. in a scrubber, or it is passed to a purifier to remove the impurities contained. If the fluorine content does not decrease when the cell is kept producing fluorine in this manner (with destruction or purification of the produced impure fluorine) but reaches the original fluorine content level again, it is again taken for the production of the pure fluorine (for example, by valve switch). Thus, the apparatus and the method of fluorine manufacture of the present invention differ from processes of the state of the art in that the contamination with impurities is prevented which obviates respective purification steps which otherwise would be necessary.

Moreover, during the production, the current efficiency can be measured for each cell by the means for independently measuring current efficiency of fluorine generating cell, for example, a flow meter. Decreases in current efficiency should indicate short circuits in the cell. As to the current efficiency measurements, it is essential to know the current put into the electrolysis during a time period (this gives a theoretical amount of fluorine which should have been produced during this period). By measuring the flow of the gas mixture and the content of F₂ in it the produced amount of fluorine in a time period is determined. The relation of produced amount of fluorine and the theoretical produced amount of fluorine during the time period is multiplied by 100 and results in the current efficiency in %. The percentages which are missing are due to recombination reactions between F₂ and H₂ inside the fluorine generating cell and the electrolytic formation of O₂, OF₂ and all losses of F₂ and/or current maybe due to short circuits. When the current efficiency decreases in the fluorine generating cell said fluorine generating cell can be separated from the line delivering produced F₂. The cell may be shut down for maintenance or repair, or the cell may be kept operating and the F₂ produced can be discarded until F₂ is produced regularly; then, the cell can be reconnected.

In one aspect, the present invention provides an apparatus for producing a high-purity fluorine gas, comprising at least one fluorine generating cell and at least one fluorine generating cell detector for detecting components of products obtained by the fluorine generating cell, wherein at least one of the fluorine generating cells is connected with the fluorine generating cell detector. It has to be noted as pointed out above that the fluorine generating cells are electrolytic cells.

Preferably, the apparatus contains at least 2 electrolytic cells. More preferably, it contains at least 6 electrolytic cells. An apparatus with at least 8 electrolytic cells is very suitable. The apparatus may even contain more electrolytic cells, e.g. ten or more. The apparatus is preferably constructed such that, if desired, additional electrolytic cells can be added if the demand for fluorine gas is rising. The cells preferably comprise jackets through which cooling water can be circulated. The advantage of providing several electrolytic cells is that the separation and possible shut-down of one or even more cells for maintenance or repair can be compensated by raising the output other cells.

In the present invention, the fluorine gas preferably is a high-purity fluorine gas.

The apparatus according to the invention optionally, further comprises control means for independently opening or closing said fluorine generating cell. Valves are very suitable to open or separate each of the cells.

As to the fluorine generating cell, all types of the fluorine generating cells used routinely in this field can be used in the present invention. Preferably, the fluorine generating cell is an electrolysis cell producing fluorine by electrolysis of a molten electrolyte. Generally, fluorine gas is generated from the fluorine generating cell. The fluorine generating cell body is generally made of metals or metal alloys resistant to HF and F₂, especially Ni, Monel, carbon steel, or the like. The fluorine generating cell body is filled with a molten electrolyte, for example, a mixed molten salt, for example, comprising a potassium fluoride-hydrogen fluoride system (i.e. “KF-HF system”) as an electrolytic bath, which can be regenerated by feeding suitable raw material, in particular HF. The fluorine generating cell body generally comprises an anode chamber and a cathode chamber. Fluorine gas is generated when electrolysis is conducted by applying a voltage between an anode disposed within the anode chamber and a cathode disposed within the cathode chamber, wherein feeding of raw material can be carried out continuously or periodically.

In one embodiment of the present invention, the fluorine generating cell includes an anode, preferably a carbon anode.

The electrolytic cells are connected to collectors for the F₂ and the H₂ produced. Typically, each cell comprises 20 to 30 anodes. Electric power is supplied to the anodes by rectifiers. The apparatus often will have a cooling water circuit supplying cooling water to the jackets of the cells.

Optionally, a settling box for F₂ and a settling box for H₂ are connected with each of the cells. The settling boxes serve to reduce the gas velocity of the F₂ and H₂ produced in the cell to avoid electrolyte dust to be carried over. Preferably, the settling boxes comprise a vibrator and a heating to melt the separated electrolyte dust for easy removal.

In another embodiment of the present invention, the fluorine generating cell detector is used for detecting impurities present in the fluorine obtained by the fluorine generating cell. If several fluorine generating cells are contained in the apparatus—which is the preferred embodiment—a cell detector is allocated to each fluorine generating cell, or a detector is used which allows the detection of several cells or all cells simultaneously or at least in quick succession.

In another embodiment of the present invention, the fluorine generating cell detector comprises:

-   (a) a sampler operable to withdraw a sample from the product     obtained from the fluorine generating cell; -   (b) a scrubber for destroying any fluorine and HF from the sample     and producing a gas stream optionally containing impurities, in     particular CF₄; -   (c) a means for detecting impurities contained in the gas stream     recovered from the scrubber, in particular a GC detector such as     flame ionization detector, thermal conductivity detector,     TDL-spectroscopy, FTIR or other detectors used routinely in this     field.     -   For example, a multi-mirror FT-IR apparatus may be used to         analyze the samples withdrawn from the gas stream produced by         several cells simultaneously.

In an embodiment of the present invention, the fluorine generating cell detector is used for detecting CF₄ present in the fluorine obtained by the fluorine generating cell. As described above, the fluorine gas stream is treated such that fluorine and HF are removed and CF₄ remains in the gas stream; it is the main component and can be analyzed, e.g. by a GC detector, a flame ionization detector, thermal conductivity detector, TDL-spectroscopy, FTIR or other detectors used routinely in this field.

In another embodiment of the present invention, the fluorine generating cell detector is a UV analyzer. With UV measurement provided for each fluorine generating cell it is feasible to produce nearly impurities-free fluorine gas without interruption in spite of using carbon anodes, wherein in particular the impurities refer to CF₄. An apparatus with a UV detector which may operate with UV light in the ranges given above, especially using a wavelength of about 280 nm is especially preferred. As described above, UV light in this range of wavelengths serves to monitor the F₂ content, but nevertheless may be used to identify anode burns with respective increase of contaminants, for example, of CF₄. The advantage is that the CF₄ content can be determined indirectly by analyzing and monitoring the F₂ content without the need for purifying operations as described for the alternative embodiment above.

In another preferred embodiment of the present invention, the fluorine generating cell detector is an on-line, semi-online or at-line detector.

In the present invention, “online” means that the whole fluorine gas goes through the detector; “semi-online” means that part of the fluorine gas is forced through the detector and that this part is combined with the main stream after analyzing; and “at-line” means that part of the fluorine gas generated is taken out of the main stream and the analyzed part of the fluorine stream is treated, collected or otherwise used after analysis.

In the preferred embodiment of the present invention, each fluorine generating cell independently is connected with a fluorine generating cell detector, or several cells are connected with a detector, as mentioned above, capable of monitoring several samples simultaneously or in quick succession.

In another embodiment of the present invention, the fluorine generating cell detector or cell detectors is connected with the control means. As to the control means, all types of the means used routinely in this field can be used in the present invention, in particular a valve or switch.

For example, the cell detector or detectors may be connected to a control board which is also connected to the valve, valves, switch or switches, the rectifier and other parts of the apparatus. In case of the detection of a decrease of the F₂ content (which is an indication of an irregular performance of the respective fluorine generating cell, possibly caused by anode burn), the control board may issue optical and/or acoustic warnings, or it may close the valve or valves automatically and thus, separate the respective cell from the others and thus prevent contamination of the F₂ produced by the other cells which function in a regular manner.

In one embodiment of the present invention, the apparatus further comprises a NaF tower. In the NaF tower, HF can be absorbed by passing gas through it. Especially, F₂ gas produced can be passed through the NaF towers to remove HF from it. The towers can be regenerated by applying heat and passing a purge gas through it.

In one embodiment of the present invention, the apparatus further comprises a particle filter. It was observed that the fluorine gas produced often contains solidified electrolyte salt which is entrained. The particle filter may be a porous body made from material which is resistant to HF and fluorine. Filters having pores with a diameter of, for example, up to 10 nm are very suitable. The fluorine gas may additionally be treated in a washer operated with liquid HF, for example, a jet scrubber.

In another embodiment of the present invention, the apparatus comprises a means for monitoring and controlling current efficiency of fluorine generating cells, for example, a flow meter. The current efficiency preferred is measured for each cell by the above means. During production of fluorine gas, if the current efficiency decreases, said fluorine generating cell can be closed (separated from the other cells), for example, by using the control means.

According to another aspect, the invention relates also to a process for manufacturing fluorine comprising use of the apparatus according to the invention as described herein before. In particular, the invention relates to a method for producing a high-purity fluorine gas comprising use of the apparatus according to the invention as described herein before.

Furthermore, the present invention relates to the use of the apparatus according to the invention in a semiconductor processing system, in a system for processing photovoltaic cells, or a system for the processing of TFTs (thin film transistors, used for liquid crystal displays), and especially, the use of the above apparatus in a process chamber cleaning system. It is well known that chambers used for said purposes, often undesired deposits form on the inner walls, parts inside the chamber and lines connected to the chamber. These deposits can be removed by treatment with fluorine gas, optionally diluted with inert gas, for example, N₂, O₂ and/or Ar, thermally or under assistance by a plasma.

In another embodiment of the present invention, the fluorine generating cell detector, especially UV analyzer, which is in combination with a NaF tower, and can be used as an indicator that only fluorine and HF (no CF₄, C₂F₆ etc.) leave in the fluorine generating cell.

In another aspect, the present invention concerns a method for monitoring impurities, such as CF₄, in manufacturing a high-purity fluorine gas by using a fluorine generating cell detector, for example, a UV analyzer. The fact that the fluorine concentration can be used to indirectly monitor the CF₄ content is surprising and also advantageous because one has to perform one measurement to detect two impurities which otherwise would need two detectors.

In a still further aspect, the present invention concerns a method for detecting an anode burn in preparing a high-purity fluorine gas using fluorine generating cell detector, for example, a UV analyzer.

In still another aspect, the present invention relates to a process for the manufacture of a semiconductor, of a photovoltaic cell or a TFT, comprising (a) manufacturing fluorine by the present invention as described herein before or the apparatus of the present invention as described herein before; (b) feeding the fluorine obtained into a semiconductor processing system, a system for processing a photovoltaic cell or a system for processing a TFT. The term “processing” includes especially steps of etching the semiconductor, photovoltaic cell and TFT with elemental fluorine and the cleaning of process chambers during the manufacture of semiconductors, photovoltaic cells and TFTs.

The present invention also relates to a process for cleaning a process chamber, comprising (a) manufacturing fluorine by the present invention as described herein before; (b) feeding the fluorine obtained into a process chamber cleaning system.

Moreover, in another aspect, the present invention provides a method for monitoring of the fluorine produced of fluorine generating cells with FTIR and/or UV, especially, carried out by at-line, semi-online or online measurement.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a brief view schematically showing an embodiment of an apparatus for producing high-purity fluorine gas of the present invention using on-line fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell.

FIG. 2 is a brief view schematically showing another embodiment of an apparatus for producing high-purity fluorine gas of the present invention using semi-online fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell.

FIG. 3 is a brief view schematically showing another embodiment of an apparatus for producing high-purity fluorine gas of the present invention using at-line fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell.

FIG. 4 is a brief view schematically showing further embodiment of an apparatus for producing high-purity fluorine gas of the present invention using fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell.

FIG. 5 is an embodiment of UV spectrogram of the fluorine gas.

DETAILED DESCRIPTION FOR CARRYING OUT THE INVENTION

Hereinafter, the present invention is described in considerable detail. The following examples are offered by way of illustration to help those skilled in the art to understand the present invention, and are not intended to limit the scope of the invention.

Apparatus of the Invention

FIG. 1 is a brief view schematically showing an embodiment of the apparatus for producing high-purity fluorine gas of the present invention using on-line fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell. In FIG. 1, the apparatus for producing a high-purity fluorine gas comprises a system 1 for feeding raw materials; system 1 preferably comprises at least one HF (hydrogen fluoride) storage tank which serves to store HF and to deliver it to the electrolytic cells.

The apparatus comprises at least one fluorine generating cell 2, and a fluorine generating cell detector 6 for detecting components of products obtained by the fluorine generating cell; optionally, a control means 3 for independently opening or closing said fluorine generating cell 2, a means 5 for independently measuring current efficiency of fluorine generating cell 2, a particle filter 4, a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same.

Particularly, the system 1 for feeding raw materials is connected with the fluorine generating cell 2; the fluorine generating cell 2 is connected with an optional control means 3; the control means 3 is connected with an optional particle filter 4; the particle filter 4 is connected with a means 5 for independently measuring current efficiency of fluorine generating cell; the means 5 is connected with a fluorine generating cell detector 6; the fluorine generating cell detector 6 respectively is connected with a system 7 for treating or purifying fluorine produced and a system 8 for treating or purifying impure fluorine gas and then collecting the same. Moreover, a system 7 is connected with a system 9 for discharging and collecting the fluorine. In addition, the system 7 or the system 8 can be, for example, is a scrubber containing an aqueous alkaline solution.

FIG. 2 is a brief view schematically showing another embodiment of the apparatus for producing high-purity fluorine gas of the present invention using semi-online fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell. In FIG. 2, the apparatus for producing a high-purity fluorine gas comprises at least one fluorine generating cell 2, and a fluorine generating cell detector 6 for detecting components of products obtained by the fluorine generating cell; optionally, a control means 3 for independently opening or closing said fluorine generating cell 2, a means 5 for independently measuring current efficiency of fluorine generating cell 2, a particle filter 4, a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same.

Particularly, a system 1 for feeding raw materials is connected with the fluorine generating cell 2; the fluorine generating cell 2 is connected with an optional control means 3; the control means 3 is connected with an optional particle filter 4; the particle filter 4 is connected with a means 5 for independently measuring current efficiency of fluorine generating cell; the means 5 is respectively connected with a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same, and a fluorine generating cell detector 6 optionally via an optional particle filter 4; the fluorine generating cell detector 6 is respectively connected with a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same. Moreover, a system 7 is connected with a system 9 for discharging and collecting the fluorine.

FIG. 3 is a brief view schematically showing another embodiment of the apparatus for producing high-purity fluorine gas of the present invention using at-line fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell. In FIG. 3, the apparatus for producing a high-purity fluorine gas comprises at least one fluorine generating cell 2, and the fluorine generating cell detector 6; optionally, a control means 3 for independently opening or closing said fluorine generating cell 2, a means 5 for independently measuring current efficiency of fluorine generating cell 2, a particle filter 4, a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same; and a system 10 for treating or collecting fluorine.

Particularly, a system 1 for feeding raw materials is connected with the fluorine generating cell 2; the fluorine generating cell 2 is connected with an optional control means 3; the control means 3 is connected with an optional particle filter 4; the particle filter 4 is connected with a means 5 for independently measuring current efficiency of fluorine generating cell; the means 5 is respectively connected with a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same, and a fluorine generating cell detector 6 optionally via an optional particle filter 4; the fluorine generating cell detector 6 is connected with a system 10 for treating or collecting fluorine. Moreover, a system 7 is connected with a system 9 for discharging and collecting the fluorine.

FIG. 4 is a brief view schematically showing a further another embodiment of the apparatus for producing high-purity fluorine gas of the present invention using fluorine generating cell detector for monitoring components of products obtained by the fluorine generating cell, wherein the fluorine generating cell detector, especially UV analyzer, also can be used as an indicator that only fluorine and HF (no CF₄, C₂F₆ etc.) leave in the fluorine generating cell. In FIG. 4, the apparatus for producing a high-purity fluorine gas comprises at least one fluorine generating cell 2, and a fluorine generating cell detector 6 for detecting components of products obtained by the fluorine generating cell; optionally, a control means 3 for independently opening or closing said fluorine generating cell 2, a means 5 for independently measuring current efficiency of fluorine generating cell 2, a particle filter 4, a NaF tower 11, a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same.

Particularly, a system 1 for feeding raw materials is connected with the fluorine generating cell 2; the fluorine generating cell 2 is connected with an optional control means 3; the control means 3 is connected with an optional particle filter 4; the particle filter 4 is connected with a means 5 for independently measuring current efficiency of fluorine generating cell; the means 5 is respectively connected with a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same, and a fluorine generating cell detector 6 optionally via a NaF tower 11, an optional particle filter 4 and a means 5; the fluorine generating cell detector 6 is respectively connected with a system 7 for treating or purifying fluorine produced, a system 8 for treating or purifying impure fluorine gas and then collecting the same. Moreover, a system 7 is connected with a system 9 for discharging and collecting the fluorine.

FIG. 5 is a UV spectrogram of the fluorine gas. As it can be seen from the FIG. 5, at about 280 nm no potential impurity of fluorine (CF₄, C₂F₆, C₃F₈ . . . , O₂, N₂, N₂O, COF₂, CO₂, OF₂, SO₂F₂, SF₆, SiF₄, HF . . . ) has UV absorption of significance. Consequently, UV detection in the F₂ UV absorption band, in particular at a wavelength of 270-290 nm, even about 280 nm is particularly preferred in the present invention.

The apparatus schematically described in FIGS. 1 to 4 may comprise more than 1 electrolytic cell which generates F₂. For example, the apparatus may comprise 8 fluorine generating electrolytic cells 2 a, 2 b, 2 c, 2 d, 2 e, 2 f, 2 g and 2 h which are connected to the system 1 delivering raw material, e.g. HF. Each of these cells 2 a to 2 h may be connected to the system 1. To each of the cells 2 a to 2 h, a respective control means, e.g. a valve, 3 a to 3 h is allocated. This allows to close one of the cells 2 a to 2 h while the other cells can continue to produce F₂. The apparatus further may contain 1 or more particle filters. Preferably, if the apparatus comprises a multitude of electrolytic cells, it may comprise detectors 6 a, 6 b, 6 c, 6 d, 6 e, 6 f, 6 g and 6 h each of which analyzes the fluorine gas produced by one of the cells 2 a . . . 2 h; alternatively, the detector 6 may comprise a detector which can analyze the fluorine gas from the cells 2 a to 2 h separately and in quick succession. The fluorine gas leaving the cells 2 a to 2 h may be passed through a manifold and then into a common line.

A comparable arrangement of the apparatus with a multitude of electrolytic cells 2 a to 2 h is preferred in the apparatus of FIGS. 2 to 4.

Method of the Invention

In order to describe the present method, FIG.1 is used as a reference. In FIG. 1, raw materials HF is fed into at least one fluorine generating cell(s) 2 independently through a system 1 for feeding raw materials, and then the fluorine gas is obtained in the cell or cells 2. The fluorine gases obtained passes through a control means 3 for independently opening or closing said fluorine generating cell or cells 2, a particle filter 4 and a means 5 for independently measuring current efficiency of fluorine generating cell, and then is fed into the fluorine generating cell detector 6, which independently detects and analyzes the fluorine gas from each fluorine generating cell 2; preferably, one fluorine generating cell detector 6 is allocated to each fluorine generating cell and thus, one detector 6 detects the fluorine gas from one fluorine generating cell.

The fluorine generating cell detector 6 is used to monitor the composition of the produced fluorine. When the fluorine generating cell detector 6 detects an anode burn, for example, slightly elevated HF content, a extremely elevated CF₄ content (C₂F₆ and COF₂ also increased, while OF₂ amount decreased) or a decrease of the measured fluorine content (for example more than 0.1 vol %-0.5 vol %), which are measured by FTIR, GC and/or UV, the fluorine generating cell(s) is(are) separated from the production of the pure fluorine and observed if the fluorine content further decreases, for example, the valve to the system 8 for treating or purifying impure fluorine gas and then collecting the same is opened while the valve to the system 7 for treating or purifying fluorine produced is shut. If its fluorine content continues to decrease, the fluorine generating cell(s) 2 is (are) shut down (e.g. current=0 A), optionally, which can be repaired, for example, exchanged by fluorine generating cell, anode and so on. If the fluorine content does not continue to decrease but reaches the original fluorine content level again, the fluorine generating cell(s) 2 is (are) again taken for the production of the pure fluorine, for example, the valve to the system 7 for treating or purifying fluorine produced is opened again while the valve to the system 8 for treating or purifying impure fluorine gas and then collecting the same is closed. Then, the fluorine produced is discharged from the system 7 into the system 9 for discharging and collecting the fluorine.

EXAMPLES Example 1

Ten fluorine generating cells 2 filled with KHF₂ electrolyte, and the fluorine gas is produced by electrolysis in the 10 cells 2. The fluorine gases obtained pass through a switch 3 for independently opening or closing said fluorine generating cell 2, a particle filter 4 and a flow meter 5 for independently measuring current efficiency of fluorine generating cell, and then are fed into a UV analyzer 6 detecting UV adsorption at 280 nm, which the UV analyzer 6 independently detects each fluorine generating cell. When the fluorine generating cell detector (UV analyzer) 6 detects a decrease of the measured fluorine content being more than 0.1 vol %, the valve to the scrubber system 8 for destroying impure fluorine gas is opened while the valve to the purification section 7 is shut down. If its fluorine content continues to decrease, the fluorine generating cells 2 are shut down (e.g. current=0 A) by the switch 3. If the fluorine content does not continue to decrease but reaches the original fluorine content level again, or after maintenance or repair, the valve to the purification section 7 is opened again while the valve to the scrubber system 8 for destroying impure fluorine gas is closed, wherein the system 8 is filled with aqueous alkaline solution. Then, the fluorine produced is discharged from the scrubber 7 into the system 9 for discharging and collecting the fluorine.

The result is shown in Table 1.

Example 2

Same as Example 1, except five fluorine generating cells 2 are used as indicated in Table 1.

Example 3

Same as Example 1, except the decrease of the measured fluorine content is more than 0.5 vol % as indicated in Table 1.

Example 4

Same as Example 2, except the decrease of the measured fluorine content is more than 0.5 vol % as indicated in Table 1.

TABLE 1 Numbers of Decrease of the Maximum CF₄ fluorine measured fluorine content in fluorine generating cells content production Example No. used (vol %) (ppmv) 1 10 0.1 111 2 5 0.1 250 3 10 0.5 555 4 5 0.5 1250

It can be seen from the examples, using the present method or the present apparatus, a production site for pure fluorine consisting of 10 fluorine generating cells can continuously be run with a maximum CF₄ content of less than 111 ppmv.

Moreover, it can be seen from the examples, using the present method or the present apparatus, a production site for pure fluorine consisting of 5 fluorine generating cells can continuously be run with a maximum CF₄ content of less than 250 ppmv.

It can also be seen from the examples that using an apparatus with a higher number of cells is advantageous. Finally, the maximum content of CF₄ is in a lower range if the respective cell is separated from the others if the F₂ content decreases by 0.1 vol %, compared to 0.5 vol %.

While various modifications and alterations within the technical sphere of the concept of this invention can be devised by the individual skilled in the art, it should be understood that such modifications and alterations also fall within the scope of this invention.

Should the disclosure of any patents, patent applications, and publications which are incorporated herein by reference conflict with the description of the present application to the extent that it may render a term unclear, the present description shall take precedence. 

1. An apparatus for producing a fluorine gas, comprising at least one fluorine generating cell, and at least one fluorine generating cell detector for detecting components of products obtained by the fluorine generating cell, wherein at least one of the fluorine generating cells is connected with the fluorine generating cell detector.
 2. The apparatus according to claim 1, wherein the fluorine generating cell detector detects impurities presented in the fluorine obtained by the fluorine generating cell.
 3. The apparatus according to claim 1, wherein the fluorine generating cell detector comprises: (a) a sampler operable to withdraw a sample from the product obtained from the fluorine generating cell; (b) a scrubber for destroying any fluorine and HF from the sample and producing a gas stream optionally containing impurities; (c) a means for detecting impurities contained in the gas stream recovered from the scrubber.
 4. The apparatus according to claim 1, wherein the fluorine generating cell detector detects CF₄ present in the fluorine obtained by the fluorine generating cell.
 5. The apparatus according to claim 1, wherein the fluorine generating cell detector is a UV analyzer.
 6. The apparatus according to claim 5, wherein the UV analyzer operates with UV light in a range of 250 to 330 nm.
 7. The apparatus according to claim 1, comprising two or more fluorine generating cells wherein each fluorine generating cell is independently connected with the fluorine generating cell detector.
 8. The apparatus according to claim 1, further comprising a control means for independently opening or closing said fluorine generating cell.
 9. The apparatus according to claim 8, wherein the fluorine generating cell detector is independently connected with the control means respectively.
 10. A method for producing a fluorine gas, comprising providing the apparatus for producing fluorine gas according to claim 1, and further comprising electrolysis of a molten compositions comprising KF and HF in the at least one fluorine generating cell to produce the fluorine gas, wherein components of products obtained by the fluorine generating cell are detected by the at least one fluorine generating cell detector.
 11. (canceled)
 12. (canceled)
 13. A process for manufacturing a semiconductor, a photovoltaic cell, or a thin film transistor (TFT), comprising a step (a) wherein fluorine is produced by the method according to claim 10 and comprising a step (b) selected from the group consisting of: feeding the fluorine obtained in step (a) into a semiconductor processing system, a system for processing a photovoltaic cell, or a system for processing a thin film transistor to etch the semiconductor, the photovoltaic cell, or the thin film transistor with elemental fluorine; and feeding the fluorine obtained in step (a) into a process chamber cleaning system to clean a process chamber used during the manufacture of the semiconductor, the photovoltaic cell, or the thin film transistor.
 14. (canceled)
 15. (canceled)
 16. The apparatus according to claim 5 wherein the UV analyzer operates with UV light in a range of from 270 to 290 nm.
 17. The method of claim 10 wherein the fluorine generating cell detector is a UV spectrometer.
 18. The method of claim 17 wherein UV absorption between 270 and 290 nm is measured to monitor the increase and decrease of the F₂ concentration.
 19. The method of claim 18 wherein, after the detection of a decrease of more than 0.1% by volume of the fluorine content, the fluorine generating cell is separated from the production.
 20. The method of claim 19 further comprising shutting down and repairing the fluorine generating cell when the fluorine content decreases further.
 21. The apparatus of claim 3 wherein the means for detecting impurities is selected from the group consisting of a gas chromatography (GC) detector, a thermal conductivity detector, a tunable diode laser (TDL) spectrometer, and a Fourier Transform IR (FTIR) detector. 